This invention relates to improvements in testing fluid-containing systems, in particular but not exclusively to the periodic, for example annual, testing of road tankers and transportable cargo tanks such as ISO tanks.
Road tankers generally haul a storage tank which includes a number of fluid storage compartments and a plurality of output pipes for delivering fluid from the storage compartments. In the case of a storage tank adapted for the transport of volatile liquids, such as fuels, the tank is also generally provided with a vapour recovery manifold for introducing recovered vapours to the storage compartments when the is fuel is being delivered.
It will be appreciated that, both for economical and environmental reasons, it is considered important that the compartments, including the storage compartments and the outlet pipes and/or the vapour recovery manifold, are ensured to be fluid-tight. Thus, legislation currently provides that a storage tank must be tested periodically to ensure its integrity.
The method currently used for testing such storage tanks is one in which each of the valves (in some cases as many 40 valves) associated with the storage tank compartment are to be removed and bench-tested for leakage and efficacy of operation, and refitted if found to be sound. In addition, the tank itself is periodically tested for leakage.
The current practice for performing the tests is based on a hydro-static principle, in which the valves are bench-tested using dedicated testing equipment, and in which the soundness of the tank is tested using water towers providing a head pressure height of approximately 3 meters of water in and above the storage compartments.
Various problems are associated with the current testing practice. The time taken to perform a full test is approximately 3 days. Precision is difficult to obtain in the testing method used. Large amounts of water are necessary to perform the tests. A full test will involve approximately 35,000 liters of water per road tanker, which, due to residues remaining in the tank at the time of testing, becomes contaminated during the test and must be decontaminated, which is costly.
In accordance with the present invention there is provided a method of testing a fluid-containing system comprising means for forming a plurality of compartments including a compartment A and a compartment B separated by valve means which are liable to leak, said method comprising:
fluidly sealing said compartment A with respect to said compartment B;
disposing said compartment A at a first gas pressure;
disposing said compartment B at a second gas pressure which is different to said first gas pressure; and
monitoring pressure within said compartment A and/or said compartment B in order to determine whether said first separating means is subject to leakage.
Thus, it is possible to test the valve means separating the compartments A and B in the system in situ. In the prior art method, since the valves are bench-tested, it cannot in fact be guaranteed that the valves when in place on the tank are indeed fluid-tight. Furthermore, by using gas pressure, the wastages involved in hydro-static testing can be avoided.
The method preferably involves said system further comprising a compartment C separated from said compartment A by second means which are liable to leak, said method further comprising:
fluidly sealing said compartment A with respect to said compartment C;
disposing said compartment C at a third gas pressure, different to a gas pressure in said compartment A; and
monitoring pressure within said compartment C and/or said compartment A in order to determine whether said second separating means is subject to leakage.
Thus, it is possible to test the first and second separating means contemporaneously, whilst maintaining a gas pressure within compartment A if appropriate. The separating means may be a valve, which is closed during the testing, or a wall common to the compartments under test.
Preferably, the first gas pressure is one of positive or negative in relation to atmospheric pressure, and the second and/or third gas pressures are the other of positive or negative in relation to atmospheric pressure. Accordingly, a pressure differential which is greater than either of the individual gas pressures with respect to atmosphere can be achieved. This is advantageous insofar as it is often unsafe to exceed individual gas pressures in compartments of a storage tank substantially above or below xc2x1200 Mb, whereas a pressure difference of above that amount may be desired in testing a valve or wall.
Furthermore, by using a combination of positive and negative gas pressures, it is possible to discount monitored pressure variations which are due to variations in the ambient temperature or pressure. If on the one hand there is leakage between the compartments, the positive pressure will reduce and the negative pressure will tend towards atmospheric pressure. If on the other hand variations are attributable to ambient temperature or pressure changes, both pressures will generally tend towards, or away from, absolute vacuum.
The gas pressure used during a stage of testing in one of the compartments may be equal to atmospheric pressure, thus avoiding the need to pressurize or de-pressurize the compartments at that stage.
According to a further aspect of the invention there is provided a method of testing a fluid-containing system comprising means for forming a plurality of compartments, said method comprising setting up a set of pressure differences between said compartments in order to test first characteristics of said system, and subsequently changing at least one of said set of pressure differences between said compartments in order to test second characteristics of said system.
Thus, different characteristics of the tank may be tested by the sequential arrangement of different sets of pressure differences between compartments in the tank. A storage tank which includes a relatively large number of interconnected compartments can then be tested throughout. For example, the initial set of pressure differences may be such that the fluid-tightness of one or more of the compartments is initially testable, and the changed set of pressure differences may allow different of the compartments to be tested for fluid-tightness.
On the other hand, the first characteristics to be tested may include a fluid-tightness characteristic, and the second characteristics to be tested may include a pressure release characteristic of a pressure release valve in the same compartment, which is to be performed using a different pressure in the compartment.
According to a further aspect of the invention there is provided a method of testing a fluid-containing system comprising means for forming a plurality of compartments including a first compartment separated from a second compartment by first means, and a third compartment separated from said second compartment by a second means, said method comprising disposing said second compartment at a first gas pressure in order to test said first separating means at a desired pressure difference between said first and second compartments, and subsequently disposing said second compartment at a second gas pressure in order to test said second separating means at a desired pressure difference between said second and third compartments.
Thus, it is possible to test both the first and second separating means at desired pressure differences.
According to a yet further aspect of the invention there is provided a method of testing a pressure relief valve for a fluid storage compartment after a period of use, comprising increasing or reducing the pressure in said compartment by introducing or removing gas into or from said compartment, and monitoring said pressure until said pressure relief valve releases, noting the pressure inside said compartment at which said release occurs, and comparing said release pressure with an expected release pressure to determine whether said valve is functioning acceptably.
Thus, the pressure release characteristics of a pressure release valve may be tested in situ after a period of use of the storage compartment.
According to a still further aspect of the invention there is provided a storage compartment comprising one or more valve(s) which are operable during normal usage of said compartment, and further comprising means for defining an aperture for passing a pressurising fluid between said compartment and a pressure change means located outside said compartment, said aperture-defining means being provided solely for the purpose of allowing the testing of said compartment, including said one or more valve(s), by use of said pressure change means.
Thus, all of the valves which are operable during normal usage of the compartment may be fully tested in situ, whilst the aperture-defining means may be chosen whereby access is gained to the interior of the compartment to be of a type which is assured to be fluid-tight when closed.
In accordance with a related aspect there is provided a method of testing a storage compartment having a plurality of replaceable valves attached thereto which require testing for integrity, said method comprising testing all of said valves whilst attached to said compartment, by introducing and/or monitoring a pressure change in said compartment via an aperture defined by means which do not require testing for integrity.
In accordance with a further aspect there is provided a valve for attachment to a storage compartment, said valve comprising means for forming a spring-biassed seal with opposing means on said compartment, and means for defining an aperture for passing a pressurizing fluid between said compartment and a pressure change means located outside said compartment, said aperture-defining means allowing the testing of said seal, by use of said pressure change means, whilst said seal is formed.
Thus, although it will be possible to remove the valve in order to provide access to the interior of the storage compartment whereby pressurizing fluid may be passed between the compartment and a pressure change means, it would then not be guaranteed that, when the valve is replaced, the compartment remains fluid-tight. By use of this aspect of the invention, the valve whereby access is achieved to the interior of the compartment may be tested in situ and may thus be assured to be fluid-tight after testing.
According to a yet further aspect of the invention there is provided a kit for testing a storage compartment for fluid-tightness, said kit comprising a pressure sensor having a desired sensitivity and means for fluidly connecting said pressure sensor to said storage compartment, said connecting means comprising damping means for absorbing instantaneous fluctuations in pressure in said connecting means which exceed said desired sensitivity.
Thus, by providing a damping means for absorbing instantaneous fluctuations, for example as caused by instantaneous barometric fluctuations or temperature fluctuations in the connecting means, a stabilized read out of enhanced accuracy may be achieved. The damping means preferably comprises a coil of tubing which expands or contracts in response to the instantaneous fluctuations, thereby preventing the instantaneous fluctuations being transmitted in full to the pressure sensor.